1. Field of the Invention
The present invention relates to a generator to be mounted in a vehicle and, more particularly, a voltage regulator with a surge absorbing capacitor element of such a generator.
2. Description of the Related Art
Usually, a generator mounted in a vehicle is composed of a stator core in which an armature coil is mounted, an engine-driven rotor in which a field coil is mounted, a rectifying unit which converts ac power generated by the armature coil to dc power, a voltage regulator which regulates output voltage of the generator, etc.
Such a regulator usually adopts a duty-ratio control system to control field current to be supplied to the field coil. In such a duty-ratio control system, electric surges are sometimes generated during switching operation. Such electric surges may cause harsh noise of audio devices and severe malfunction of other electronically controlled devices. In order to suppress such electric surges, a surge absorbing capacitor element has been introduced into the generator as disclosed in JP-A-2000-209824 or U.S. Pat. No. 6,236,557 B1, a counterpart of the former.
However, such a capacitor element is usually accommodated in a voltage regulator case, which is disposed near the rectifier unit. Therefore, the capacitor element is exposed to high temperature of the rectifier unit caused by switching and rectifying operation. In addition, the capacitor element is indirectly heated by the armature coil and the field coil in operation.
The capacitor element is mainly composed of an aluminum deposited polyester film, which may deteriorate if exposed to high temperature for a long time period. Although there is an idea of replacing the polyester film by a more heat-resistive film such as a polyphenilene sulfide film, this is too expensive.